Spinneret block with readily exchangable nozzles for use in the manufacturing of spun-blown fibers

ABSTRACT

The present invention relates to a particular execution for a die block for spun-blowing process for forming a fibers or filaments that may further form a spun-blown web or nonwoven comprising such a formed spun-blown web, e.g. as a layer in a multi-layer 5 composite web. The die block comprises nozzles that are readily removable, and preferably chamfered.

FIELD OF THE INVENTION

The present invention relates to an equipment adapted to create filaments of the spun-blown type for forming nonwoven materials of superior quality as well as to a process for operating such equipment.

BACKGROUND

Spunmelt is a process where fibers are spun from molten polymer through a plurality of nozzles in a die head connected to one or more extruders for being formed into web, such as nonwoven webs or as components thereof. The spunmelt processes are well known in the art, and may include melt-blowing, see e.g. U.S. Pat. No. 8,017,534 (K-C, Harvey), spun-bonding, see e.g. U.S. Pat. No. 5,935,512 (K-C, Haynes).

From such technologies, a “hybrid” technology, often referred to as “spun-blowing” has been developed and described in e.g. WO2015/171707/U.S. Pat. No. 9,303,334 (Biax, 2014). This technology provides a number of benefits with regard to the fiber and web properties, but also with regard to the equipment and process for the manufacturing. However, the equipment is quite inflexible with regard to replacement of individual nozzles, as in case of uneven wear of the nozzles over time, or if varying filament diameter were to be executed.

Thus, from U.S. Pat. No. 6,364,647 it is known to construct a similar spun-blowing apparatus wherein the nozzles are removable. Whilst this provides certain improvements with regard to operation but also with regard to product flexibility, such a design carries a disadvantage of sharp transition from the polymer supply system into the nozzle capillary, which results in turbulences of the polymer flow, not only reducing smoothness of the flow through the capillary, but also increasing the propensity for polymer depositions around the nozzle opening that may require more frequent cleaning.

Henceforth, it is an object of the present invention to overcome problems of the spun-blowing technology.

SUMMARY

The present invention is a die block for forming spun-blown filaments comprising

-   -   molten polymer supply;     -   air supply;     -   a spinneret block comprising         -   an upper plate comprising a polymer supply side, and         -   a lower plate, and         -   a plurality of nozzles;     -   an air distribution plate comprising openings;     -   an exterior air plate comprising openings;     -   a cover strip     -   securing means.

The spinneret block, the air distribution plate, the exterior air plate, and the cover strip are mounted in this order and secured by the securing means such that

-   -   the nozzles protrude through corresponding openings in the air         distribution plate and further through corresponding openings in         the exterior air plate, and     -   such that polymer passageways are formed for molten polymer         passing from the polymer supply side of upper plate through the         nozzles; and     -   such that air passageways are formed for air passing from the         air supply through openings in the air distribution plate and         the exterior air plate.

The openings in the exterior plate and the nozzles are adapted so as to allow molten polymer exiting the nozzles and air flowing through the openings of the exterior air plate are at an angle of less than 30°, preferably less than about 10° and more preferably essentially parallel.

Further, the spinneret body comprises

-   -   an upper plate positioned towards the molten polymer supply,         comprising         -   a polymer supply cavity         -   and upper plate openings exhibiting at least at their lower             end an upper plate opening diameter;     -   a lower plate positioned away from the molten polymer supply,         comprising lower plate through holes concentric to the upper         plate through holes exhibiting         -   an upper portion positioned towards the upper plate with an             upper portion diameter, optionally with an upper portion             chamfering, and an upper portion length         -   and a lower portion positioned opposite of the upper portion             with a lower portion diameter and a lower portion length,             whereby the upper portion diameter is larger than the lower             portion diameter.

The nozzles comprise

-   -   an upper section exhibiting an upper section outer diameter     -   and a lower section exhibiting a lower section outer diameter;     -   a capillary as an inner through hole through the nozzle.

Further, the upper sections of the nozzles fit removably into the upper portions of the lower plate, preferably without protruding therefrom, wherein further the upper plate opening diameter and the lower plate opening diameter or the chamfering exhibit a difference of less than 50 μm, preferably less than 20 μm.

The die block may further satisfy one or more of the conditions selected from the group consisting of

-   -   the inner diameter of the nozzle being less than about 1.25 mm,         preferably less than about 0.8 mm;     -   the outer diameter of the nozzle being less than about 2 mm;     -   the nozzle exhibiting a length of less than about 50 mm;     -   the nozzle exhibiting a length of more than about 10 mm;     -   the nozzle exhibiting a L/d ratio of less than about 50;     -   the nozzle is executed with a pre-hole exhibiting a diameter of         more than about 0.5 mm;     -   the nozzle is executed with a pre-hole exhibiting a pre-hole         diameter of less than about 4 mm;     -   the nozzle exhibits transition zones between the sections of         differing diameters which extend more than 2 mm, preferably more         than about 4 mm;     -   the nozzle exhibits transition zones between the sections of         differing diameters which extend less than about more than 2 mm,         preferably more than about 4 mm;     -   the nozzle is executed with a pre-hole exhibiting a length of         more than 2 mm, preferably more than 4 mm, whereby this length         includes the length of a transition zone towards a larger         diameter;     -   the nozzle is executed with a pre-hole exhibiting a length of         more than 2 mm, preferably less than about 20 mm, preferably         less than about 14 mm, more preferably less than bout 8 mm,         whereby this length includes the length of a transition zone         towards a larger diameter;     -   the die block exhibiting a CD width of more than 250, preferably         more than 1500, even more preferably of more than about 2000 mm         or even more than 5000 mm.

Optionally, the openings in the upper plate of the die block satisfy one or more of the conditions selected from the group consisting of

-   -   comprising a chamfering at a chamfering angle of between 30° and         60° or with a rounded profile,     -   exhibiting a chamfering diameter of between 1.5 to 4 times the         inner diameter of the capillaries,     -   exhibiting a length of more than about 2 mm, preferably more         than about 4 mm,     -   exhibiting a length of less than about 20 mm, preferably less         than about 14 mm more preferably less than about 8 mm, and most         preferably a length of about 6 mm;     -   tapering from the polymer supply side towards the opposite side.

The nozzles of the die block may form an array and further comprise stationary pins, preferably exhibiting the same outer diameters and lengths as a nozzle, the stationary pins being positioned at the periphery of the array.

The upper plate of a die block may further comprise

-   -   at least one row groove         -   positioned on the side towards the first plate and         -   oriented parallel to the row of nozzles,     -   and optionally a circumferential groove circumscribing the         nozzle row or the array of nozzles, respectively,

wherein

-   -   at least one row of nozzle holes is, preferably two rows of         nozzle holes are, positioned in a row groove, thereby forming         the chamfering section of the nozzles, and     -   the grooves are adapted to receive a sealant.

The sealant compound may be adapted to prevent in an assembled state of the die block the flow of the molten polymer

-   -   into nozzle holes which are positioned in the row groove(s),     -   along the gap between the first and the second plate of the die         body towards neighbouring row grooves, or nozzle holes, or the         outside.

The grooves may exhibit a rounded cross-sectional shape or at least a rounded base, preferably a cross-sectional shape of a partial oval with a half-circular base and straight sides above.

The grooves may exhibit one or more of the dimensions selected from the group consisting of

-   -   a width of more than about 1 mm, preferably more than about 2         mm,     -   a width of less than about 10 mm, preferably less than about 5         mm,     -   a depth of more than about 1 mm, preferably more than about 2         mm,     -   a depth of less than about 10 mm, preferably less than about 5         mm.

The grooves may comprise a sealant which may be selected from the group consisting of acrylic resins, adhesive sealants, butyl rubber, elastic sealants, epoxy thermosets, latex sealants, plastic sealants, polysulfide sealants, polyurethane sealants, rubber sealants, silicone sealants, preferably polysiloxanes, or fluorocarbon polymers, such as PTFE, or urethane sealants, more preferably of the silicon or PTFE type.

The array of nozzles of a die block may comprises at least two sub-arrays comprising nozzles differing from nozzles of a different sub-array in at least one of the dimensions selected from the group consisting of

-   -   inner diameter of the nozzle;     -   outer diameter of the nozzle,     -   length of the nozzle.

Optionally, the array of nozzles of the die block comprises at least two sub-arrays, each of the sub-arrays being connected to a separate polymer supply system adapted to supply molten polymer to the sub-array differing in at least one of the features selected from the group consisting of

-   -   polymer type;     -   polymer flow rate;     -   polymer pressure;     -   polymer temperature.

In another aspect, the present invention is a process for forming a nonwoven web comprising spun-blown fibers, comprising the steps of

-   -   providing equipment according to any of the preceding claims,     -   providing a thermoplastic polymer for forming melt-blown fibers,         exhibiting a MFI from 30 to 2000 for 10 minutes at 2.16 kg at         appropriate material class temperature, preferably at 210° C.         for polypropylene and 190° C. for polyethylene, and     -   forming filaments by applying a pressure of less than 70 bar,         preferably less than 50 bar more preferably less than 45 bar at         the polymer supply.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 shows a spun-blowing equipment according to prior art.

FIG. 2 shows a melt-blowing equipment according to prior art with removable nozzles.

FIG. 3 A to F depict schematically particular features of the present invention.

FIGS. 4 to 7 depict particular executions according to the present invention.

Same numerals in the figures depict same or equivalent features. Figures are schematic and not to scale.

DETAILED DESCRIPTION

The present invention relates to a particular execution for a die block for spun-blowing process for forming fibers or filaments that may further form a fibrous spun-blown web or nonwoven comprising such a formed spun-blown web, e.g. as a layer in a multi-layer composite web.

Spunmelting is a process where fibers are spun from molten polymer through a plurality of nozzles of a die head connected to one or more extruders. The spunmelt process may include melt-blowing, spun-bonding and the hybrid process as described hereinafter in more detail, also referred to as spun-blowing.

Melt-blowing is a process for producing very fine fibers typically having a diameter of less than about 10 microns, where a plurality of molten polymer streams are attenuated using a hot, high speed gas stream once the filaments emerge from the nozzles. The attenuated fibers are then collected on a collector, e.g. a flat belt or drum collector. A typical melt-blowing die has around 35 nozzles per inch and a single row of nozzles. The typical melt-blowing die uses inclined air jets at each side of the row of nozzles for attenuating the filaments.

Spun-bonding is a process for producing strong fibrous nonwoven webs directly from thermoplastics polymers by attenuating the spun filaments using cold, high speed air while quenching the fibers near the spinneret face. Individual fibers are then laid down randomly on a collection belt and conveyed to a bonder to give the web added strength and integrity. Fiber size is usually below 250 μm and the average fiber size is in the range of more than about 10 microns and/or less than about 50 microns. The fibers are very strong compared to melt-blown fibers because of the molecular chain alignment that is achieved during the attenuation of the crystallizing (solidifying) filaments. A typical spun-bond die has multiple rows of polymer holes and for a conventional polymer of the polypropylene type the polymer melt flow index (MFI) is usually below about 500 grams/10 minutes at 2.16 kg load.

The present invention is related to a hybrid process between a conventional melt-blown process and a conventional spun-bond process, using a multi-row spinneret similar to the spinneret used in spun-bonding except the nozzles are arranged to allow parallel gas jets surrounding the spun filaments in order to attenuate and solidify them. Each of the extruded filaments is shrouded by pressurized gas and its temperature can be colder or hotter than the polymer melt. Optionally, the periphery around the array with the filaments may be surrounded by a curtain of pressurized gas.

In order to explain the general principles of the spun-blowing equipment and process for forming filaments and further webs, such as nonwoven webs or components of such webs, express reference is made to U.S. Pat. No. 9,303,334 describing such a technology in greater detail. Thus, FIG. 1 depicts a die block for such a conventional “hybrid” spun-blowing process.

Overall, a die block 26 comprises as elements a spinneret body 52, an air distribution plate 70, an exterior plate 78, and a cover strip 88. Further, nozzles 58 extend from the spinneret body 52 through openings of the distribution plate 70 and exterior plate 78, respectively, such that molten material can pass through the capillary 60 of the nozzle 58 to form filaments 86 at the tip of the nozzle 96.

For ease of explanation, the order of the elements referred to in the following is such that the spinneret body 52, the air distribution plate 70, the exterior plate 78, and the cover strip 88 are arranged along gravity, such that the spinneret body 52 is positioned above and secured to the air distribution plate 70, which is positioned above and secured to the exterior plate 78, which is positioned above and secured to the cover strip 88, with securing means not shown.

FIG. 1 shows a cross-sectional view of the die block 26. When positioned into a manufacturing equipment for forming nonwoven, this view corresponds to an x-z-directional view, with the x-direction 12 denoting the manufacturing direction, i.e. the direction of movement of the resulting web, and the z-direction 15 corresponding to the height (along gravity). In the execution as depicted, the three nozzles 58 represent one “column” of the “multi row” (here three-row) die block 26. The die block comprises a plurality of columns positioned y-directionally adjacently 18 (i.e. perpendicularly to the plane of drawing and indicated by the circle) such that the columns and rows of nozzles form an array of nozzles of a die block. A spinneret body 52 can contain from as few as ten nozzles 58 to several thousand nozzles 58. For a commercial size line, the number of nozzles 58 in the spinneret body 52 can range from between about 500 to about 10,000.

The number of rows can vary as well as the number of columns. Typically, the number of rows will be more than 1, often more than 5, and will be less than about 30, or even less than 15. Typically, the number of columns will be more than 50, but can be more than about 200, and may be less than 3500.

As described in US'334, the nozzles 58 are formed of capillary tubes that are inserted through openings in the spinneret body 52 to form a passageway for the molten polymer.

Each of the nozzles 58 has an inside capillary diameter and an outside diameter. The inside diameter can range from between about 0.125 mm to about 1.25 mm. The outside diameter of each nozzle 58 should be at least about 0.5 mm. The outside diameter of each nozzle 58 may range from between about 0.5 mm to about 2.5 mm.

Typically, the length of a nozzle 58 ranges from between about 0.5 to about 6 inches.

As the molten polymer needs to pass only through the capillaries of the nozzles, US'334 describes the tubes to be tightly fitted and typically welded to the spinneret body, which represents an important difference, when compared to the present invention, as will be described in more detail herein below.

The molten material 22, as may be a thermoplastic polymer of the homopolymer type or a mixture of different polymers, is heated to a temperature well above its melting point, in case of propylene based polymers typically to at least about 170° C., often to about 210° C., upstream of the die block 26, usually in an extruder (not shown). Optionally, different polymers may be directed to respectively different groups of nozzles.

The polymer throughput through each nozzle 58 is stated in “gram per hole per minute” (“ghm”). The polymer throughput through each nozzle 58 can range from between about 0.01 ghm to about 4 ghm.

At its top, i.e. on the upper spinneret body side oriented towards the polymer supply, the die block 26 has a cavity 30 and an inlet 28 connected to the cavity 30. The molten material 22 is conveyed along the polymer passageway from inlet 28 towards the upper portion of the spinneret body 52, and further via the nozzles downwardly. The spinneret body 52 also has one or more gas passages 32 formed therethrough for conveying pressurized gas (air) to an air chamber 54, which is essentially formed between the spinneret body 52 and the air distribution plate 70. The plurality of nozzles 58 extend downwardly from the spinneret body allowing molten material to flow through the capillaries 60 for exiting the nozzles and the die block downward of the exterior plate at nozzle tip 96 in the form of filaments 86.

Further, a plurality of stationary pins 62 may surround the array of nozzles, affixed to the spinneret body and extending through openings of the air distribution plate into the openings of the exterior air plate.

Each of the stationary pins 62 is an elongated, solid member having a longitudinal central axis and an outside diameter. Each of the stationary pins 62 is secured to the spinneret body 52 and usually they have a similar outside diameter to the polymer nozzles 58. The outside diameter of each of the stationary pins 62 should remain constant throughout its length. The dimension of the outside diameter can vary. The outside diameter of the stationary pins 62 may be more than about 0.25 mm, or more than about 0.5 mm, or more than about 0.6 mm, or even more than about 0.75 mm.

An air distribution plate 70 is secured to the spinneret body 52 having a plurality of openings. Each one of first openings 72 accommodates one of the nozzles 58. If stationary pins 62 are employed, they are accommodated in second openings 74, and each of the third openings 76 is located adjacent to the first and second openings, 72 and 74 respectively. When operating the process, pressurized gas, typically air, is flowing along air passageways from the air chamber 54 through openings 72, which are a thin annulus around the nozzles, openings 74, also a small annulus around the stationary pins, if present, and third openings 76 as a main passageway for the air.

An exterior air plate 78 is secured to the air distribution plate 70, away from the spinneret body 52. The exterior member 78 has a plurality of first openings 80 surrounding the nozzle 58. Second enlarged openings 82 surround each of the stationary pins 62, if present.

In operation, the molten polymeric material 22 is extruded through each of the nozzles 58 to form multiple filaments 86 which are intended to be shrouded from the ambient air by the pressurized gas, typically though not necessarily air, emitted through the first enlarged openings 80, formed in the exterior member 78, at a predetermined velocity essentially parallel to the axis of the capillaries 60 and hence the flow direction of the filaments 86 at the nozzle tip 96

The pressurized gas (air) flow exiting the second enlarged openings 82 formed in the exterior member 78 around the stationary pins, if present, forms a further shrouding air flow, which is also oriented essentially parallel to the axis of the nozzles, and hence also essentially parallel to the filaments exiting the nozzles, aiming at isolating the filaments 86 from surrounding ambient air, as indicated in FIG. 1 with the arrow 94.

In U.S. Pat. No. 6,364,647 (hereinafter referred to as US'647) a system is described (see FIG. 2) wherein individual nozzles 58 of the array of nozzles are removable from the spinneret body 52. To this end, the nozzles 58 are equipped at their upper end (towards the polymer supply 22, which is further covered by upper cover 53) with shoulders 51, such that they can firmly rest in the wider portion of holes through the spinneret body 52. This provides a number of benefits, such as the flexibility of exchanging individual nozzles, when they are worn out. It also allows to implement and quickly introduce nozzles of differing capillary diameters.

During operation, the nozzles are pressed into the respective openings by the pressure of the molten polymer.

However, this system still carries a disadvantage of sharp transition from the polymer supply chamber 22 into the plurality of nozzle openings.

As a consequence, deposits of polymeric material may form around the inlet of the capillaries, which may degrade over time and require more frequent cleaning.

FIG. 3A depicts the principle of the present invention, by showing in a schematic cross-sectional view a die block 126 comprising spinneret block 152, air distribution plate 170, exterior air plate 178, cover strip 188, and securing means 199 arranged in the same way as described in the context of FIG. 1. Also shown are an inlet cavity 130 for molten polymer 122, an air inlet and distribution chamber 132 (the air supply means not being shown). The spinneret block 152 comprises an upper plate 151 and a lower plate 155, with “upper” denoting positioning towards the polymer supply and “lower” away therefrom, as shall apply throughout the present description. Nozzles 158 are inserted into the lower plate 155 of the spinneret body, forming a polymer passageway that goes from the inlet cavity 130 through the capillaries 160 of the nozzles 158 towards the nozzle tip 196, where the filaments are formed. However, a skilled person will readily realize that the vertical orientation is not essential, but the die block may be tilted around a CD oriented axis such that nozzles may be oriented relative to the vertical at more than 5°, or 15°, or 30°, or 45° or even more, but typically less than about 90°.

FIG. 3B shows schematically an enlarged portion from FIG. 3A, focusing on the positioning of nozzles 158 in openings through the lower plate 155 and the relative positioning of openings through the upper plate 151, and FIG. 3C and D show schematically an enlarged cross-sectional view particular executions of a single nozzle 158.

A plurality of nozzles 158, in FIG. 3A eight are exemplarily shown, may be arranged in columns and rows forming an array of nozzles as described in the above for US'334, each exhibiting an inner diameter 157, corresponding to the diameter of the capillary 160 for the molten fluid flow. The inside diameter can be more than about 0.125 mm and/or less than about 1.25 mm. The nozzle 158 is formed in two sections an upper section 331 and a lower section 335, differing in their outer diameter whilst the inner diameter of the capillary 160 remains essentially constant. At its upper end, the capillary 160 may have a chamfering 333, preferably with a chamfering angle of at least 30° and/or less than 60°, as indicated in FIG. 3C, or with a rounded profile as indicated in FIG. 3D. The outside diameter 159 of the lower section 335 of the nozzle 158 can be more than about 0.5 mm and/or less than about 2.5 mm. The outside diameter 161 of the upper section 331 may be more than about 0.5 mm and/or less than about 5 mm.

Typically, the overall length 330 of a nozzle 158 may be more than about 20 mm and/or less than about 150 mm. The length 332 of the upper section 331 may be more than about 1 mm and/or less than about 50 mm, and the length 334 of the lower section 335 may be more than about 10 mm and/or less than about 140 mm.

Each nozzle 158 is fitted into an opening 360 of the lower plate 155 that has an upper portion 361 and a lower portion 365.

The upper portion 361 is adapted to receive the upper section 331 of the nozzle 158 and exhibits a diameter 362, which is not more than 2 mm wider than the outer diameter 161 of the upper section of nozzle 158. For a good fit, the diameter 362 is less than 50 μm or even less than 10 μm more than the outer diameter 161 of the upper section of the nozzle, and it may even be slightly smaller, such as less than 10 μm smaller, such as when the nozzle is fitted with force or at lower temperature.

The lower portion 365 is adapted to receive the lower section 335 of the nozzle 158 and exhibits a diameter 366, which is not more than 2 mm wider than the outer diameter 159 of the lower section of nozzle 158. For a good fit, the diameter 366 is less than 50 μm or even less than 10 μm more than the outer diameter 159 of the lower section of the nozzle, and it may even be slightly smaller, such as less than 10 μm smaller, such as when the nozzle is fitted with force or at lower temperature.

The transition from the upper portion 361 of the opening 360 to the lower portion 365 is preferably a sharp one, though a small radius or chamfering is acceptable. However, this transition should be matched with the transition from the upper section 331 of the nozzle to its lower section 335.

Most preferably, the length 332 of the upper section 331 of the nozzle 158 may be the same as the length 364 of the upper portion 361 of the opening 360, such that the differential 369 is zero, though the differential may be less than 10 μm, or less than about 2 μm. A negative differential (i.e. the nozzle protruding out of the hole) is not preferred.

The length 368 of the lower portion 365 of the opening 360 may be more than about 2 mm and/or less than about 100 mm.

The upper plate 151 of the spinneret body 153 comprises openings 370 that are aligned with the axis 339 of the capillary 160 of the nozzle 158, and hence with the openings in the lower plate 155. The opening 370 exhibits at its lower end a diameter 372 that matches as much as possible the diameter of the capillary 160 or—if present—of the chamfering 333.

Preferably, the difference between these diameters is less than about 20 μm more preferably less than about 10 μm. Also, the offset of the axis of the opening 370 from the axis of the capillary is most preferably essentially zero, but preferably less than 5 μm or less than 50 μm. Optionally and often preferably, the opening 370 has a chamfering 375 at its upper end, preferably at an angle of at least 1°, or 10°, or 30°, or 60° and/or less than 90° or any angle among these values. Thus, in the extreme the chamfering may extend over the full length of the upper plate, such that the cross-sectional view of the opening may correspond to a trapeze, as indicated by dotted lines 376 in FIG. 3B and in FIG. 3E.

During operation, the openings 370 function as pre-holes for the capillaries and preferably exhibit a diameter of more than about 1.5 and/or less than about 4 times the diameter of the capillary and a length corresponding to the thickness of the upper plate of more than about 2 mm and/or less than about 20 mm.

Such a pre-hole provides a smoother flow from the cavity with the molten material into the capillary 160, which in turn will widen the opportunity for a wider process window for the process.

Also, it is also with the scope of the present invention that the die block may—in addition to the nozzles as described in the above—comprise stationary pins, as described in the context of US'334 in the above. FIG. 3F depicts schematically such a pin that with its outer dimensions may correspond to a nozzle 158, except for having no capillary but being solid.

In yet a further variant of the present invention allowing to broaden the operating range of the equipment, the chamfering may be executed as grooves. To this end, the spinneret body is executed non-unitary in two parts, namely a first plate, also referred to as taper plate, comprising a polymer supply side, and a second plate positioned opposite of the polymer supply side. The second plate comprises grooves on the surface towards the first plate, which are oriented parallel to the row of nozzles.

FIG. 4 depicts—similarly to FIG. 3A—in FIG. 4A a spinneret body with a first or “upper” plate 151 positioned with its molten polymer receiving cavity 130 towards the polymer supply and 4B in FIG. 4B a second or “lower” plate 155, positioned on the opposite side of the polymer receiving cavity 130 of the first or upper plate 151. The second plate further comprises four row grooves 140, each for two nozzles, and a circumferential groove 145.

FIG. 4B depicts a portion of a second plate 155 of a spinneret body with a cross-sectional view along the rows of the nozzles rows, here showing eight holes, as may represent holes 156, adapted to receive removable nozzles (not shown). Further, row grooves 140 are shown, that extend parallel to the nozzle rows, exhibiting preferably a rounded cross-sectional shape or at least a rounded base execution, here shown exemplarily exhibiting a cross-sectional shape of a partial oval with a half-circular base and straight sides above. Preferably, a groove exhibits

-   -   a width of more than about 1 mm, preferably more than about 2         mm,     -   a width of less than about 10 mm, preferably less than about 5         mm,     -   a depth of more than about 1 mm, preferably more than about 2         mm,     -   a depth of less than about 10 mm, preferably less than about 5         mm.         between 1 mm and 12 mm, preferably between 2 and 5 mm.         Preferably the depth is between 1 mm and 10 mm, preferably         between 2 and 5 mm. Preferably, the width and the spacing of the         grooves are selected such that the nozzle rows are spaced apart         equidistantly.

Generally, each row groove may belong to at least one row of nozzles, preferably two rows of nozzles belong to one row groove, as depicted in the figure. Preferably, though not necessarily, all row grooves comprise nozzle holes 156, more preferably each row grove comprises two rows of nozzle holes 156. Thus, for the exemplary execution in FIG. 4B, eight rows of nozzles holes are positioned in four row grooves,

Preferably, the second plate 155 of the spinneret block further comprises closed circumferential groove 145, parallel to the row grooves as well as perpendicular thereto to circumscribe the nozzle array. Preferably, the x-y-directional corners of the circumferential groove 145 are rounded. Preferably, though not necessarily, the circumferential groove exhibits the same cross-sectional shape as the row grooves.

The holes in the second plate are adapted to receive nozzles in the variant of removable nozzles, and the wider opening of the row grooves provides the chamfering effect as described in the above allowing a smooth flow of the molten polymer.

Further, the grooves 140 and 145 are adapted to receive a sealant, allowing to fill selected grooves but also any gap that may be formed between the first and the second plate of the spinneret block. For the row grooves, this allows to block the polymer flow into the nozzle holes and further into the capillaries of the nozzles connected to this row groove. Even further, it allows to prevent the flow from one groove to the neighbouring one, as otherwise might occur through a gap between the first and the second plate. Thus, by application of the sealant, rows of nozzles can be “switched off”, as depicted in FIG. 4C, with grooves 140′ and 145 being filled with a sealant, and grooves 140″ being unfilled, allowing molten polymer to pass through. Similarly, the sealant in the circumferential groove prevents outward leakage of the polymer material.

For the sealant material the key requirement is that it withstands the operating temperatures, i.e. it does not flow into the capillaries or into the gap at the elevated temperatures, and thus should not be fluid up to temperatures of about 100° C., preferably 180° C., more preferably more than 230° C. or even more than 500° C. or more. Thus, the sealant may be selected from the group consisting of acrylic resins, adhesive sealants, butyl rubber, elastic sealants, epoxy thermosets, latex sealants, plastic sealants, polysulfide sealants, polyurethane sealants, rubber sealants, silicone sealants, e.g. polysiloxanes, fluorocarbon polymers, such as PTFE, or urethane sealants, with silicones and PTFE being preferred, and PTFE being most preferred. An exemplary sealant may be “PTFE wire 3.2 mm”, as commercially available from ATAG Spa, Italy.

Preferably, though not necessarily, a fluid or pasty sealant undergoes curing after being applied and the spinneret block is assembled, though pre-cured materials may be used as well, such as O-rings of appropriate size.

Preferably, and in particular for fluid or pasty sealants, the amount of sealant is selected so as to slightly overfill the groove, so as to enable squeezing of small amounts of the sealant into the gaps between the first and the second plate. This feature is particularly beneficial for relatively thin second plate, as may be less than about 20 mm, more preferably less than about 10 mm, or even less than about 8 mm. During assembly or operation, such relatively thin plates may slightly deform such that without any sealant molten polymer may ooze outwardly or into a neighbouring groove.

Further, the sealant is adapted to be removed from the grooves and from the holes or capillaries, if penetrated there into, when the spinneret block is disassembled. This removal can be made pure mechanically, or by blowing air or liquid though the holes or capillaries, or by any other means not damaging the structure.

The benefit of grooves filled with grooves is essentially to allow to widen the operating range of the die block.

It is known that it is preferred from an operational perspective, but also for good product quality to maintain the polymer flow through a capillary within a relatively narrow range. However, for different products or product types, different web basis weights are desired. However, when switching from, e.g. a lower basis weight, e.g. 35 g/m², to a higher one, e.g. 60 g/m², the flow rate through the capillaries may be increased, which requires higher operating pressures, hence cost, but also may deteriorate the quality of the resulting fibers, e.g. by increased stress applied to the polymer molecules. Henceforth, a conventional approach is to replace the complete spinneret block by another one with a different number of nozzle rows. This implies a high effort both with regard to work for this change over, but also with regard to maintaining a stock of replacement part. As to the latter, the nozzles represent a significant part of the costs. Henceforth it is beneficial to keep a minimum of replacement part—as enabled by this aspect of the present invention. To this end, a die block is designed for the upper range of throughput, as exemplarily and for explanatory purposes only with twelve rows of nozzles, with which a high basis weight product can satisfactorily be produced. When a lower basis weight product is to be made, the outermost row grooves, each connected to two nozzles, may be filled with sealant, such that only 8 nozzles are operational, and lower basis weights may be made without product quality deterioration. For even lower basis weight, two more row grooves may be filled, only 4 nozzle rows will now be operational.

In order to avoid deadspace, which may lead to deterioration of the polymer, it is preferred to adapt the holes in the first plate 151 of the spinneret body to the number of non-filled grooves, as depicted in FIG. 4D, corresponding to the execution shown in FIG. 4C, such that holes through first plate 151 that would lead to the filled grooves 140′ in FIG. 4D are omitted. However, the replacement of several of such plates is significantly easier and less costly compared to a complete spinneret block.

Optionally, the array of nozzles may comprise sub-arrays. Such a sub-array may include at least one row of nozzles, preferably, though not necessarily extending over the full width of a die block.

Referring to FIG. 4, a first execution of a die block comprising one or more sub-arrays, the nozzles of at least one of the sub-arrays differ substantially from nozzles of a different sub-array in at least one of the dimensions selected from the group consisting of inner diameter of the nozzle, outer diameter of the nozzle, and length of the nozzle, in FIG. 4 indicated by varying inner nozzle diameter for bigger nozzles 158′ forming a first array compared to smaller nozzles 158″ forming a second array. Within the present context, the term “substantially different” refers to a difference in the respective dimension of at least 5%, often more than 10% thereof.

In a further execution as depicted in FIG. 5, but not exclusive to the other executions, the nozzles of one sub-array may be connected to a first, separate polymer supply system via a first molten polymer supply cavity 130′ adapted to supply a first type of molten polymer to the first sub-array differing from the molten polymer supplied to a different sub-array via a second molten polymer supply cavity 130″, whereby the polymers differ in at least one of qualitative features as polymer type, or quantitative parameters such as polymer flow rate, polymer pressure, thereby differing by at least 5%, often more than 10%, or polymer temperature, thereby differing by at least 5° C. Optionally, the nozzles may be executed with co-axially positioned sub-capillaries so as to create bi- or multi-component fibers, wherein such sub-capillaries are supplied with different, respectively immiscible polymer types.

This process window is primarily dictated by

-   -   pressure of the molten polymer in the cavity;     -   temperature of the molten polymer;     -   diameter of the capillary;     -   outer diameter or the nozzle, impacting the air flow and the air         flow ratio;     -   length of the capillary;     -   material properties of the molten polymer, as expressed by the         Melt Flow Index (MFI), as may be determined by ASTM D1238 and         ISO 1133, and for polypropylene as a polymer that suitably can         be processed with the current equipment and process, it is         suitably expressed in units of gram per 10 minutes at 210° C.         and 2.16 kg load, whilst for other material classes the         temperature is set to the appropriate temperature, e.g. 190° C.         for polyethylene.

As a comparative example, the equipment and the process as described in US'334 exhibiting

-   -   a capillary inner diameter of 0.46 mm;     -   a capillary length of 24 mm;     -   hence an L/d ratio of about 52;         and could be operated at a temperature of about 210 C.° with a         back pressure of 50 to 70 bar for a molten polymer with an MFI         of less than about 500 [g/10 min @ 2.16 kg load].

In order to achieve comparable fiber dimensions and properties, the equipment of the present invention present invention exemplarily exhibited

-   -   a capillary diameter of 0.46 mm;     -   a capillary length of about 18 mm:     -   a pre-hole diameter of about 1.2 mm:     -   a pre-hole length (including a 60° chamfering at the inlet and         at the transition to the capillary) of about 6 mm;     -   henceforth an L/d ratio for the capillary of about 39, which         further allowed to employ a polypropylene polymer exhibiting an         MFI of about 500 [g/10 min @ 2.16 kg load] of a back pressure of         significantly lower than 50 bar.

One benefit of subjecting the polymer to a lower backpressure is that the reduction of the mechanical stress results in allowing to produce stronger nonwovens.

In other terms, the present invention provides an equipment that can exhibit a lower L/d ratio, which is—for a given MFI—indicative of the flow resistance, and thusly allows to operate at a wider process window for MFI and backpressure.

Further, the smoother flow from the cavity for the molten polymer 130 to the pre-hole 370, preferably even more smoothed flow of polymer in the chamfering, significantly reduces the turbulence of polymer around the inlet and hence also polymer residue deposition, allowing longer operating times without interruption for cleaning. 

1. A die block for forming spun-blown filaments comprising molten polymer supply; air supply; a spinneret block comprising an upper plate comprising a polymer supply side, and a lower plate, and a plurality of nozzles; an air distribution plate comprising openings; an exterior air plate comprising openings; a cover strip securing means, wherein said spinneret block, said air distribution plate, said exterior air plate, and said cover strip are mounted in this order and secured by said securing means such that said nozzles protrude through corresponding openings in said air distribution plate and further through corresponding openings in said exterior air plate, and such that polymer passageways are formed for molten polymer passing from said polymer supply side of upper plate through said nozzles; and such that air passageways are formed for air passing from said air supply through openings in said air distribution plate and said exterior air plate; whereby said openings in said exterior plate and said nozzles are adapted so as to allow molten polymer exiting said nozzles and air flowing through the openings of said exterior air plate are at an angle of less than 30°, wherein said spinneret block comprises an upper plate positioned towards the molten polymer supply, comprising a polymer supply cavity and upper plate openings exhibiting at least at their lower end an upper plate opening diameter; a lower plate positioned away from said molten polymer supply, comprising lower plate through holes concentric to said upper plate through holes exhibiting an upper portion positioned towards said upper plate with an upper portion diameter, and an upper portion length and a lower portion positioned opposite of said upper portion with a lower portion diameter and a lower portion length, whereby said upper portion diameter is larger than said lower portion diameter, said nozzles comprising an upper section exhibiting an upper section outer diameter and a lower section exhibiting a lower section outer diameter; a capillary as an inner through hole through said nozzle; and wherein said upper sections of said nozzles fit removably into the upper portions of said lower plate, wherein further said upper plate opening diameter and said lower plate opening diameter or said chamfering exhibit a difference of less than 50 μm.
 2. A die block according to claim 1, satisfying one or more of the conditions selected from the group consisting of the inner diameter of the nozzle being less than about 1.25 mm; the outer diameter of the nozzle being less than about 2 mm; the nozzle exhibiting a length of less than about 50 mm; the nozzle exhibiting a length of more than about 10 mm; the nozzle exhibiting a L/d ratio of less than about 50; the nozzle is executed with a pre-hole exhibiting a diameter of more than about 0.5 mm; the nozzle is executed with a pre-hole exhibiting a pre-hole diameter of less than about 4 mm; the nozzle exhibits transition zones between the sections of differing diameters which extend more than 2 mm; the nozzle exhibits transition zones between the sections of differing diameters which extend less than 2 mm; the nozzle is executed with a pre-hole exhibiting a length of more than 2 mm, whereby this length includes the length of a transition zone towards a larger diameter; the nozzle is executed with a pre-hole exhibiting a length of more than 2 mm, whereby this length includes the length of a transition zone towards a larger diameter; the nozzle is executed with a pre-hole exhibiting a length of less than about 20 mm, whereby this length includes the length of a transition zone towards a larger diameter; the die block exhibiting a CD width of more than 250 mm.
 3. A die block according to claim 1, wherein said openings in said upper plate satisfy one or more of the conditions selected from the group consisting of comprising a chamfering at a chamfering angle of between 30° and 60° or with a rounded profile, exhibiting a chamfering diameter of between 1.5 to 4 times the inner diameter of said capillaries, exhibiting a length of more than about 2 mm, exhibiting a length of less than about 20 mm; exhibiting a length of less than 8 mm; tapering from said polymer supply side towards the opposite side.
 4. A die block according to claim 1, wherein said nozzles form an array, further comprising stationary pins, said stationary pins being positioned at the periphery of said array.
 5. A die block according to claim 1, wherein said upper plate further comprises at least one row groove positioned on the side towards said first plate and oriented parallel to said row of nozzles, and optionally a circumferential groove circumscribing said nozzle row or said array of nozzles, respectively, wherein at least one row of nozzle holes is positioned in a row groove, thereby forming said chamfering section of said nozzles, and said groove is adapted to receive a sealant.
 6. A die block according to claim 5, wherein said sealant compound is adapted to prevent in an assembled state of said die block the flow of the molten polymer into nozzle holes which are positioned in said row groove(s), along the gap between said first and said second plate of said die body towards neighbouring row grooves, or nozzle holes, or the outside.
 7. A die block according to claim 5, wherein said grooves exhibits a rounded cross-sectional shape or a rounded base.
 8. A die block according to claim 5, wherein said grooves exhibit one or more of the dimensions selected from the group consisting of a width of more than about 1 mm, a width of less than about 10 mm, a depth of more than about 1 mm, a depth of less than about 10 mm.
 9. A die block according to claim 5, wherein said row groove comprises a sealant, preferably selected from the group consisting of acrylic resins, adhesive sealants, butyl rubber, elastic sealants, epoxy thermosets, latex sealants, plastic sealants, polysulfide sealants, polyurethane sealants, rubber sealants, silicone sealants, preferably polysiloxanes, or urethane sealants, or fluorocarbon polymers, or more preferably of the silicon or PTFE type.
 10. A die block according to claim 1, wherein said array of nozzles comprises at least two sub-arrays comprising nozzles differing from nozzles of a different sub-array in at least one of the dimensions selected from the group consisting of inner diameter of the nozzle; outer diameter of the nozzle, length of the nozzle.
 11. A die block according to claim 1, wherein said array of nozzles comprises at least two sub-arrays, each of said sub-arrays being connected to a separate polymer supply system adapted to supply molten polymer to said sub-array differing in at least one of the features selected from the group consisting of polymer type; polymer flow rate; polymer pressure; polymer temperature.
 12. Process for forming a nonwoven web comprising melt-blown fibers, comprising the steps of providing equipment according to claim 1, providing a thermoplastic polymer for forming melt-blown fibers, exhibiting a MFI from 30 to 2000 for 10 minutes at 2.16 kg at appropriate material class temperature, and forming filaments by applying a pressure of less than 70 bar.
 13. A die block according to claim 1, whereby said openings in said exterior plate and said nozzles are adapted so as to allow molten polymer exiting said nozzles and air flowing through the openings of said exterior air plate are at an angle of less than about 10°.
 14. A die block according to claim 4, wherein said stationary pins exhibit the same outer diameters and lengths as a nozzle,
 15. A die block according to claim 5, wherein said upper plate further comprises a circumferential groove circumscribing said nozzle row or said array of nozzles, respectively.
 16. A die block according to claim 9, wherein said sealant is selected from the group consisting of acrylic resins, adhesive sealants, butyl rubber, elastic sealants, epoxy thermosets, latex sealants, plastic sealants, polysulfide sealants, polyurethane sealants, rubber sealants, silicone sealants.
 17. A die block according to claims 15, wherein said sealant is selected from the group consisting of polysiloxanes, urethane sealants, and fluorocarbon polymers.
 18. A die block according to claim 9, wherein said sealant is selected from the group consisting polysiloxanes, urethane sealants and fluorocarbon polymers.
 19. Process for forming a nonwoven web comprising melt-blown fibers according to claim 12, wherein in said step of providing a thermoplastic polymer for forming melt-blown fibers, the thermoplastic polymer is polypropylene, exhibiting a MFI from 30 to 2000 for 10 minutes at 2.16 kg at 210° C. or polyethylene exhibiting a MFI from 30 to 2000 for 10 minutes at 2.16 kg at 190° C.
 20. Process for forming a nonwoven web comprising melt-blown fibers according to claim 12, wherein in said step of forming filaments the pressure applied at the polymer supply is at less than 45 bar. 